[diggles]

Hello, my friend,

When I got my 645 Auto Bellows, I noticed the auto-diaphragm of all 645 Pentax lenses remains open all the time, whether they are on the "A" position or set to a particular f/number. I realized I needed a cable release on the front standard of the Bellows to close down the diaphragm, otherwise all pictures would be taken wide-open. I had previously used my 645 FA 400 mm f/5.6 with my Pentax K1 body for fall pictures and I just now realized they were shot with the lens wide-open (they were not too bad in 24X36 format but could have been way better with the aperture closed to f/11 or f/16, had I been aware of this fact at the time). My question is : When using 645 lenses, how do you make sure your diaphragm closes to a middle aperture (let's say f/11) with your Actus which, I suspect, has no means to close down the 645 lenses apertures ? Pentax 67 lenses' diaphragms can be closed manually but not the 645s'. The 645 lens diaphragm has to be "actively" closed by the 645 camera body.


Regards

Hello Richard L.,

You can get a Pentax 645 lens plate for the Cambo Actus. It has a manual lever for controlling the aperture that uses a 0-10 scale. It also works on the Pentax 645 lenses that do not have a manual aperture ring.

Actus Lensplate with Pentax 645 Lens Bayonet – Digital Back

You can use the 1-10 scale on the lens plate to set your aperture although it's not ideal because the numbers don't correspond to a specific aperture. I do understand why they did it that way since every lens has a different range.

If you want to use the aperture ring to set the f/stop then you can put the lens on auto before mounting it to the lens plate then move the lever on the lens plate to 10. Doing this closes the lens to the smallest aperture. Then using the aperture ring on the lens, you can open the f/stop to the setting you want for shooting.

[RICHARD L.]

Thank you for your prompt answer. At least you can control your aperture. Almost all Pentax 645 lenses come into their own around f/11. Using the 645 lenses on a Pentax K mount now seems, let's say, "pointless" if they remain wide-open all the time ... Sigh !

Regards

[texandrews]

The Actus is a pleasure to work with. It is incredibly well made, not too big, and offers a lot of versatility. I'm using it with the Fuji GFX 50s. I'm not sure if the Actus will work with the K.

I think the last time I looked there was an adapter plate for the K mount---obviously there's one for the lenses....

The 645 DFA 35mm, the 67 55mm latest and 75mm 2.8 are working very well for architectural photography…which is what I got the Actus for. I'm wanting to try out the 67 105mm f/2.4 as well.

I'm interested in the 35. How is that doing with some movements? That's about as long as would be practical for me---I'd like wider, and I have the 25, but it's massive so I wonder about mounting it, and I'm not sure about the image circle.

What I like about using the Pentax lenses is that I can also use them on my 645z for handheld photography like environmental portraits. Focusing on the fly with an EVF is awkward to me. While the quality of the Fuji GFX is fantastic, it doesn't really feel like a camera to me. It feels more like a digital capturing device. When the Pentax 645z is in my hands, it definitely feels like a camera.

Interesting distinction. I didn't have a problem with the A7R's EVF (which is how I first got interested in the Actus), but the Fuji's bothered me. The splendid OVF of the Z has certainly spoiled me.

[RICHARD L.]

I was puzzled by the fact the diaphragm of all Pentax 645 lenses remains permanently open when they are unmounted. I thought for a moment that the diaphragm didn't close at all when the lenses were mounted on a K1 or a K3 body and that pictures were always taken with a wide-open aperture. WELL, I WAS WRONG. This morning, I mounted my 645 A 120 mm f/4 Macro lens on the Pentax "645 to K-mount" adapter and put this combo on my K3 body. I turned the diaphragm ring to f/8, I checked visually and saw that the diaphragm was properly closed. I took a couple of pictures with it and they were well exposed. I'm relieved and I guess it is the adapter that permits the aperture to function manually in stop-down mode, like with older K or M lenses.

Regards



Picture of my DA 55-300 mm zoom taken with the 645 A 120 mm f/4 @ f/8 on a K3 body. Only quirk : you must "enable aperture ring use" in the MENU of the K3 to be able to trigger the shutter.
This macro lens is SHARP !

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Last edited by RICHARD L.; 08-06-2020 at 09:55 AM.

[w2ck]

Hi,

I haven't had my 645 A 120 macro long, but I really like how it works.

Stan

[barondla]

Hi,

I haven't had my 645 A 120 macro long, but I really like how it works.

Stan

Agree. My 645 A 120 macro is also doing well. The long focus helicoid is butter smooth and sharpness is great.

Thanks,
barondla

[RICHARD L.]

[RICHARD L.]

[Bassat]

Sorry, I'm a bit late to the party. You compared 2 lenses from f/5.6 to f/16, on a tripod, with a cable release? Ok. That does not surprise me; it is a good methodology for comparing results. What does surprise me is that you were expecting noticeably different results. The major differences in IQ resulting from any lens(es) arise at the extremes. An f/1.4 lens is going to be way better at f/4 than any f/4 lens.

I learned this lesson a few years ago. I used to shoot Canon full-frame bodies, and L-primes/zoom. Somewhere along the line I realized I was pay truckloads of money to get images I could acquire for a lot less money. I do most of my shooting from f/8 to f/16. In this range, lens choice makes little difference. I sold all of the full frame digital cameras, all of the L-zooms/primes. I now shoot 20+ year old Canon T2, EOS 1, and EOS 1N bodies with 20 year old consumer glass: 28-135, 70-210, 100-300, and my one concession to IQ, the Tokina 17-35 f/4.

Yes, I spend about $20 for a roll of 36 frames. I traded $15,000 worth of gear for just about $500 worth of gear. The math works out to film is costing me nothing until I get to 750 rolls processed. At 12-15 rolls per year, I am good for the rest of my life.

Oh, the other thing I've learned from going back to film: Pixel-peeping is a complete waste of time. Nobody viewing your photos will care one iota.

[rdeloe]

diggles, I want to thank you for doing this and for publishing your results. You saved me a lot of money. I am (was) in exactly the same boat as you. In fact, today I posted a request on the forum asking for exactly what you'd already done. 35mm favour - PentaxForums.com Somehow I missed your work. Richard L. immediately pointed me to this thread, where all my questions were answered.

So here's my take on this: I am not buying a D FA 35/3.5!

I downloaded all the PEF files you supplied, loaded them into Lightroom, and then did a side-by-side with the compare tool. Interestingly, I had things setup so I didn't know what file was what (so it was a blind test). One of the files was noticeably better than the other in almost every respect. I assumed it was the D FA, but in fact it was the A. This held true across the two comparison scenes that you provided. Based on what I'd read about the D FA, I was certain going into this that it would be a lot stronger than the old A.

One should always be careful in making judgements about a lens based on one copy of a len and one test scene. Also, this test is only using the central part of the image circle, so it doesn't offer any insights into how the lenses do when shifted (which is how I use Pentax 645 lenses). Nonetheless, given how expensive the D FA is, and given that I already have a really good A and can't use the autofocus capability of the D FA, it seems pointless for me to buy a D FA and do my own testing. Thanks for saving me the time and money.

[DandA]

A little late to this thread but after fairly extensive testing of all three 35mm 645 lenses, 1st on a 645D and later on the 645Z...my conclusion is the HD DFA due to extremely low field curvature, flair resistance and excellent edge to edge sharpness, espcially by f4 and beyond is my 1st choice if money is not factored in. The "A" version would definitely be considered as a best buy. I found edge sharpness at more open apertures not quite as sharp as the HD DFA , had some CA and a bit more distotion. The original FA had quite massive field curvature in comparison to the other two and sometimes an anomaly I'll call a blur dead zone. I noticed a few small roundish areas that would randomly show up in an other sharp images as soft or a blur. Even without that, I would place the original FA version last. Its field curvature was most noticable in longer distance shapts such as ladscapes, which would end up with sides and corners at long distances being very soft but the foreground corners sharp (ie: field curvature).

Dave (D&A)

[barondla]

Shooting Pentax FF and APS-c for years, I rarely encountered flare problems, short of shooting into the sun. Started thinking multicoating technology had banished flare. Not so sure about medium format. Some of my 1st Pentax HD35 lens photos have flare. Was I just unlucky, or do medium format lenses have more trouble dealing with flare?

Thanks,
barondla

[texandrews]

Shooting Pentax FF and APS-c for years, I rarely encountered flare problems, short of shooting into the sun. Started thinking multicoating technology had banished flare. Not so sure about medium format. Some of my 1st Pentax HD35 lens photos have flare. Was I just unlucky, or do medium format lenses have more trouble dealing with flare?

Thanks,
barondla

Aside from the corner softness in the FA 45 and FA 35 lenses, flare is the only other "deficit" I have found in my 645 lenses----and not all of them. I remember distinctly a shot I was trying to get in Japan and almost immediately realized it was suffering from veiling flare. In my shooting in museums where I have to contend with a lot of lights all over the place in the overall installation shots, I have not had a problem with the 25 (always forget which one I have!) DFA 28-45, DFA 35, the FA 45-85, the DFA 55, or the DFA 90. I may have used the FA 150 once or twice, but because of the shot setup and its narrow fov I wouldn't expect to see flare in my use.

Outdoors in the sculpture garden have not seen a problem with any of my lenses, and on occasion I have had to shoot in situations where I dreaded seeing flare. No issues. Bear in mind though that my aversion to flare is so strong that I go to great lengths not to be in a position to encounter it outdoors. Indoors I often have no choice.

[RICHARD L.]

Funny the way some 645 lenses get "so-so" reputations, yet when you use them appropriately (good light, solid support, critical focus and middle apertures), none of the alleged deficiencies appear in your pictures. The 645 FA 33-55 mm f/4.5 was such a lens. People said it had soft corners and lacked sharpness because of a bad case of "curvature of field" that couldn't be corrected by stopping down. But when you try it in real life, it performs splendidly. Is it just me ?

[Pål Jensen]

The 645 FA 33-55 mm f/4.5 is such a lens, reputed to have soft corners and bad performance at any aperture, yet when you try it, it performs splendidly. Is it just me ?[/B]

Have you tried it on a full frame 645?

Corners are OK if stopped down. The images below are shot with a 645NII